Different Hatching Rates of Floodwater Mosquitoes Aedes sticticus, Aedes rossicus and Aedes cinereus from Different Flooded Environments.

Abstract

Simple SummaryIn the lower Dalälven region, floodwater mosquitoes cause recurring problems during floods. Since 2002, flooded areas have been treated with Bacillus thuringiensis israelensis (Bti) to control the number of hatching floodwater mosquitoes. The area is composed of both open meadows that are grazed or mowed, as well as unmanaged open meadows and forest areas that are regularly flooded. This study compared the number of mosquito larvae that hatched from soil samples collected from these environmental categories to assess whether management of flooded areas affected mosquito abundance. The results show that fewer mosquitoes hatched from mowed meadows than from the other categories. It was further clear that Aedes cinereus were more abundant in open areas with tussocks while Aedes sticticus were dominating in forests and in open unkept areas, shrubs, and bushes. This difference is important for nuisance management since Aedes cinereus generally fly only short distances and mainly stay in the area where they hatched, while Aedes sticticus is capable to fly long distances and can cause nuisance problems in larger areas.In the lower Dalälven region, floodwater mosquitoes cause recurring problems. The main nuisance species is Aedes (Ochlerotatus) sticticus, but large numbers of Aedes (Aedes) rossicus and Aedes (Aedes) cinereus also hatch during flooding events. To increase understanding of which environments in the area give rise to mosquito nuisance, soil samples were taken from 20 locations from four environmental categories: grazed meadows, mowed meadows, unkept open grassland areas and forest areas. In each location 20 soil samples were taken, 10 from random locations and 10 from moisture retaining structures, such as tussocks, shrubs, piles of leaves, logs, and roots. The soil samples were soaked with tap water in the lab, and mosquito larvae were collected and allowed to develop to adult mosquitoes for species identification. Fewer larvae hatched from mowed areas and more larvae hatched from moisture retaining structure samples than random samples. The results showed that Aedes cinereus mostly hatch from grazed and unkept areas and hatched as much from random samples as from structures, whereas Aedes sticticus and Aedes rossicus hatched from open unkept and forest areas and hatch significantly more from structure samples. When the moisture retaining structures in open unkept areas where Aedes sticticus hatched were identified it was clear that they hatched predominantly from willow shrubs that offered shade. The results suggest that Ae. sticticus and Ae. cinereus favor different flooded environments for oviposition.